This invention relates to a driving device incorporated in a bridge laying apparatus and is of the type which has on either side a pinion which is designed to mesh with a rack mounted longitudinally along a bridge section to advance the bridge section as the pinion is rotated. Each pinion may be moved axially by a hydraulic power cylinder unit into and out of the zone of the rack.
In published International Application WO 90/05216 a bridge laying vehicle is disclosed which has a laying arm designated as a laying device and a receiving device associated with the laying device. The laying arm as well as the receiving device are provided with a driving device which is adapted to shift individual bridge sections or a plurality of interconnected bridge sections on the laying-arm and/or the receiving device. The driving devices have on either side rack-driving pinions which mesh with racks which, as a rule, are arranged along the guide rails at the lower chord of the bridge sections.
In handling bridge sections the driving devices provided with the rack-driving pinions must perform three functions:
they have to drive at least one bridge section in the longitudinal direction; PA1 they have to immobilize at least one bridge section on the laying apparatus; and PA1 they have to be releasable from all bridge sections to make possible a feed of interconnected bridge sections by the respective other drive or to make possible a lowering of a bridge section past the driving device without a collision between the rack of the bridge section and the pinion of the driving device.
For releasing the connection between the drive and the rack of the respective bridge section, German Offenlegungsschrift (application published without examination) 35 17 724 discloses an axially displaceably supported driving pinion intended to mesh with the rack, and the axial position of the pinion may be changed by a hydraulic cylinder arranged offset relative to the rotary axis. It is a disadvantage of such a solution that because of the eccentric arrangement of the hydraulic cylinder stresses and misalignments within the pinion guide box may occur and, as a result, the various functions may be adversely affected to a substantial extent.